A select committee was this morning shown several video clips recorded on the devices, including a prison brawl, a standoff between guards and an inmate, and a guard discovering a long blade used in a stabbing.

Mrs Tolley said that the footage showed the cameras could be useful for de-escalating potentially violent situations.

In one clip, a prisoner becomes agitated when asked to get off a telephone. But he backs down when he realises he is being filmed.

He tells the guards: "You're f***ing lucky you've got a camera."

Corrections chief executive Ray Smith said the technology was also useful for collecting evidence to be used in disciplinary action or court proceedings.

In another clip, a guard recovers a long blade from a sinkhole, which was believed to have been used in the stabbing of another inmate.

Mrs Tolley said the trial had been promising, but she could not yet commit to rolling out the technology in all prisons or throughout the police force.

The cameras were worn on a guards' shoulder, and once activated were capable of recovering the 30 seconds of footage before they were turned on.